When tourists come to Stora Karlso, a nature reserve surrounded by limestone off the coast of Sweden, they maintain a respectful distance from the many sea birds that live on the island. Like most visitors to wild places, they try to leave only footprints and take pictures only – to slide between the threads of the web of life they came to see.
I was not so lucky. In an article published this month in Biological Conservation, researchers detail how the sudden absence of tourists in Stora Karlso during the pandemic triggered a surprising chain reaction that devastated the island’s common murre colony, decreasing its population of newborn birds.
Stora Karlso became a nature reserve in the 1880s, after thousands of years of human occupation. Its common wall population – which has already been reduced to less than 100 because of hunting and egg collection – is now around 60,000 birds, and is the largest in the Baltic Sea.
Jonas Hentati-Sundberg, a researcher at the Swedish University of Agronomic Sciences and lead author of the new article, has been studying the colony for 19 years. When he and his team started planning the 2020 research season, they expected the pandemic to present logistical obstacles: without visitors, fewer boats would be operating and the island’s restaurant would be closed.
“Those were our main thoughts,” he said.
However, since the first trips of the year, at the end of April, they noticed that the murres “flew all the time”, with individuals sometimes disappearing for days. It was a change in behavior, he said, and a sign that something was making the birds more nervous than usual.
The island’s white-tailed eagles also changed their behavior. Typically, seven or eight eagles spend the winter there and then leave when the visiting season begins in the spring, said Hentati-Sundberg.
But without the influx of tourists, they remained, and more eagles joined them – sometimes dozens at a time. “They will gather in places where there is a lot of food and little disturbance from people,” he said. “This year, this was his hot spot.”
A further observation clarified the new dynamic: the eagles, free from the uncomfortable presence of humans, were themselves troubling the murres.
Although eagles rarely feed on murres, sea birds fear them and spread at the slightest flight. In a May video, a distant figure with wide wings sends hundreds of murres hissing and cascading off its edges, like theater spectators running out of balconies after the stage touches.
This has happened repeatedly. From May 1 to June 4, birds in part of the colony were moved from their nests by eagles for an average of 602 minutes a day – far more than the 2019 average of 72 minutes.
In addition to time, the murre colony lost eggs, kicking them off the ridges during panic takeoffs or leaving them vulnerable to hungry seagulls and crows. Twenty-six percent fewer eggs hatched in 2020 than normal for the rest of the decade.
“Emotionally, it is a little difficult to chew,” said Hentati-Sundberg.
Researchers around the world have taken advantage of travel restrictions related to the pandemic to study the effects of the sudden human absence in the natural world, an event that some call “anthropopause”. A discovery like this, in which a tourist stop has a domino effect on several species, is “fascinating,” said Nicola Koper, a professor of ecology at the University of Manitoba who was not involved in the research. “It shows how impactful our travel changes have been on entire ecosystems.”
For Dr. Hentati-Sundberg, a summer on a changed Stora Karlso emphasized how strongly we can be connected to other species – even when we see ourselves as mere observers – and that “understanding our relationships with nature and embracing the idea of ourselves as part of the picture is a more fruitful strategy ”for conservation decisions.
“Withdrawing is not an option,” he said. “We are outside.”